While the project has been interesting and I have learned a ton working through it, I feel I may have misunderstood the basic concept. It was my understanding that the pic would work without any programming having to be done to it other than setting it with the two switches. Was this an incorrect assumption?

Where I am having my specific problem is that I get no output from GP0. My guess is that I am not able to set GP0 as an output, but I don't understand why.

I have 5 volts at position + and at GP3, 10.8V at GP4 and nothing at GP5.

If you didn't program the pic, then it won't wok. The pic has to be programmed with the hex file of the compiled program that was written for it. Did you purchase the pic from the person who posted the circuit?

While the project has been interesting and I have learned a ton working through it, I feel I may have misunderstood the basic concept. It was my understanding that the pic would work without any programming having to be done to it other than setting it with the two switches. Was this an incorrect assumption?

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Yes.

Where I am having my specific problem is that I get no output from GP0. My guess is that I am not able to set GP0 as an output, but I don't understand why.

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The PIC12F629 comes programmed only with the internal clock calibration bits. You have to program it yourself.

I have 5 volts at position + and at GP3, 10.8V at GP4 and nothing at GP5.

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If you have 10.8v at GP4, you may have destroyed the PIC.

A PICs' pins should be kept within Vdd and Vss/GND unless they are being programmed. In the case of the PIC12F629, Vpp (12v for programming) is on pin 4 (GP3, MCLR\)

Yes its an incorrect assumption ,PIC12F629 is a microcontroller and it must be programmed.Normally this kind of MCU projects will give you the hex file or the source code but as its so simple it just states the off time about 0.04 sec
So in short you have to program it first

Since I have been interested in this project for a couple of years and only now have come to the place where it seems possible, I suppose I will take this next step.

Next question(s). Could you give advice on programmers and program languages? Keep in mind that I am a middle aged hobbyist with a new interest. I think Basic would be a good fit. The most inexpensive but serviceable option would be best.

Also, while I appreciate your concern over modifying external lighting, this will be additional, not primary, lighting, and has great value as an attention getter when piloting a motorcycle.

A project like this also performs the function of brain exercise - quite important for old folk.

Since I have been interested in this project for a couple of years and only now have come to the place where it seems possible, I suppose I will take this next step.

Next question(s). Could you give advice on programmers and program languages? Keep in mind that I am a middle aged hobbyist with a new interest. I think Basic would be a good fit. The most inexpensive but serviceable option would be best.

As far as programmers, if you don't want to spend much and will be staying with smaller flash PICs, you could look at the PICkit 1 from Microchip. The PICkit 2 or PICkit 3 allows you to program a great many more PICs.

Also, while I appreciate your concern over modifying external lighting, this will be additional, not primary, lighting, and has great value as an attention getter when piloting a motorcycle.

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I'll still strongly advise against it. It may seem like a simple project, but you may not understand that automotive environments are among the most brutal on the planet, electrically (high transient voltages exceeding 60v on a 12v system), temperature (-40°C to 125°C) physically (shock & vibration) and exposure to corrosive liquids/chemical and high humidity/just plain soaking wet.

Your first problem will be how to determine a method of voltage regulation that will survive peak input voltages >60v. A 7805 or LM317 regulator will simply die.

All components that you use must be rated for use over the full automotive temperature range. (-40°C to 125°C)

The circuit board must be conformal coated to protect against corrosion, secured in a suitable enclosure, and mounted to minimize the effects of shock/vibration.

You are probably planning on tapping in to your vehicle's wiring harness to get the brake light signal and power. If you are thinking of using wire nuts or electrician's tape to make splices, you should stop now while you're ahead.

Off to source a new pic or two...

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Do you know which uC's that Microchip sells which meet automotive temperature range specifications?

Are you planning on making this "third brakelight" yourself?

Most new experimenters think they can use cheap LEDs from an auction site or Asian supplier. They won't be the proper color, nor the proper viewing angle, and the specifications supplied will be dubious at best.

Before you consider taking on such a challenge, I suggest that you at least get a good bit of experience with projects "on the bench".

By the way, I don't think much of the circuit you linked to. Either the 2N2222 or the TIP41 will be toast in short order, as there is no current limiting between the 2n2222 collector and the TIP41 emitter.

No wire nuts and very little electrical tape in my splices. I did source some very nice connectors, though. Interface with the original yamaha connectors quite well.

I do appreciate your comments. I also have come to understand the cost and value of failure as a learning tool. I will succeed or fail and have a good time trying. Plus, I got a new soldering station out of the deal - and new tools are a big plus for me.

Your advice is noted. I will be keeping your environmental notes in mind and be on the lookout for a better circuit.

Please do return to have your final design or schematic peer reviewed/approved.
And when it does come time to mount this and install it on your bike, we can suggest ways that wont damage your original wiring.

Taking a tap off the break light bulb socket to trigger the circuit rather than to power it will keep your circuit from drawing too much or feeding current into the OEM setup.

An additional battery pack to run your lights, triggered by the tap, would be the safest. That way you have less worry about transients and other related problems.

That way, if your circuit dies or a component on the circuit dies short, it will not effect your OEM signals.